1. Field of the Invention
This invention relates to the field of mass spectrometry and more specifically to the field of chemical ionization mass spectrometry.
2. Background of the Invention
Chemical ionization mass spectrometry has been developed for use in laboratory and field trace gas measurements. Such mass spectrometry typically involves ionization of a neutral species by a reagent ion to yield a product ion. The product ion may be analyzed by a quadrupole mass analyzer for species identification and abundance determination.
One type of chemical ionization mass spectrometry is proton transfer-reaction mass spectrometry (PTR-MS), which has been developed for online quantification of volatile organic compounds in air, among other applications. Proton transfer-reaction mass spectrometry involves proton-transfer reactions with hydronium ions (H3O+) to ionize volatile organic compounds. The resulting protonated product ion is then detected by mass spectrometry. For instance, volatile organic compounds directly emitted from natural and anthropogenic sources in the air as well as their oxidation products may be quantified simultaneously by proton transfer-reaction mass spectrometry. A drawback to proton transfer-reaction mass spectrometry includes that it measures species based on hydronium ions, which considerably narrows the scope of applications. Further drawbacks include that other desired species may not react with hydronium ions, which may result in the failure to detect species. A drawback for other types of conventional chemical ionization mass spectrometry includes the typical need to calibrate the mass spectrometer with gas standards to quantify the species. Certain gas standards are not commercially available because of difficulties in synthesizing the species.
Consequently, there is a need for an improved method and apparatus for mass spectrometry. In addition, there is a need for improving chemical ionization mass spectrometry to reduce the non-detection of species. Further needs include an improved apparatus and method for quantifying species.